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cost-benefit approach.doc

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Breid Mc Ilkenny

• old animals made decisions thru life as it matured (settle, eat, associate) • all decisions made in environment that varies in space and time • habitat: environment in which an organism lives; seeks food, rest, nest sites, escape routes in habitat • suitable habitats: good predictors of conditions suitable for future survival+reproduction • chemosensory cue of red abalone larvae settles on surface that has potential of supplying food for future survival and reproductive success • visual info provides useful cues; presence of already settled individuals is indication • flycatchers assess quality of habitat by seeing how well neighbours are doing; (settle in areas where broods (abundant food) artificially enlarged) • some highly social animals vote on quality of habitats (worker bees dance to communicate location, site that excites most workers is chosen) • animals compete for high-quality habitats; may improve its fitness by establishing exclusive use of habitat • may do this by establishing territory which excludes conspecifics (same species) by advertising it owns area and chasing others away (but advertising and chasing takes energy) • cost-benefit approach: assumes an animal has only a limited amt of time and energy to devote to activities; [costs must not outweigh benefits]; ecologists can make predictions, design experiments, and make observations explaining why patterns evolve the way they do • benefits of behaviour are improvements in survival and reproductive success; 3 costs • energetic cost: difference btwn energy at rest and energy used to perform behaviour • risk cost: increased change of getting killed/injured when performing behaviour • opportunity cost: sum of benefits the animal forfeits by not performing other behaviours • Moore and Marler: male lizards with more testosterone spent more time patrolling territories, doing advertising displays, used 1/3 more energy than control males. They had less time to feed, got fewer insects, stored less energy, died at higher rate • some animals defend all-purpose territories that include all resources (tigers, songbirds) • food supplies cannot be defended if widely distributed or fluctuate a lot (ex oceans) • some animals defend territory used only for mating (male grouse congregate on display grounds, defending small area. Males often use so much energy that less tired males eventually evict them) • foraging theory: helps us understand survival (ultimate) value of feeding choices; benefits = nutritional value, and costs similar to those for territorial defense • more rapidly an animal captures food, more time+energy it will have for other things • characterize each type of available food item in 2 ways: time it takes animal to pursue, capture, and consume item; and by amt of energy an item contains • most valuable food type is one that yields most energy per unit of time expended o can determine rate at which an animal would obtain energy given foraging strategy o animal gains most energy by taking only most valuable type and ignoring all others; but as that type depletes, it adds less valuable types (ex fish would ignore small water fleas if there are large ones) • for bluegills, only energy content of water fleas mattered; some animals travel great distances for nutrients • some ingest food for other reasons. Frogs get poisons from eating ants that have evolved poisons as defense mechanisms b/c frogs are immune to poisons • spices in food preparation protects ppl from contaminated food; most commonly used spices inhibited growth of some food-borne bacteria; perhaps spices disguise taste/smell of spoiled food. But eating spoiled food could be dangerous, and natural selection is not likely to have favored ppl who ate rancid food, no matter how tasty • most animals associate with others for mating partners and/or for resources it controls • males initiate courtship, hardly reject receptive females, fight for females • females seldom fight and often reject males o b/c sperm are small and cheap to make, very large # of offspring, males can increase reproductive success by mating with females o b/c eggs larger and expensive than sperm, females cannot increase reproductive output by increasing # of males she mates with, but by quality of genes received from mate, resources he controls, and assistance; may cause evolution of traits • males use tactics – courtship
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